Temperature Drop Calculator for Hydronic Piping  

by the National Mechanical Insulation Committee (NMIC)


Calculates the Temperature Change of Water Flowing in a Pipe (Reference: 2009 ASHRAE HoF, Chapter 4, Equation 48, (pg 4.21))

This calculator estimates the temperature drop (or rise) of water flowing in a pipe.


(Input information may generally be be obtained from design documents or field measurements)

  • Line 1. Enter the temperature of the water entering the pipe
  • Line 2. Enter the ambient temperature (temperature of the air surrounding the pipe)
  • Line 3. Enter the wind speed of the ambient air in miles per hour
  • Line 4. Enter the flow rate of the water carried by the pipe in gallons per minute.
    Note: Calculator does not screen for reasonable flow velocities, Hydronic piping is normally sized for flow velocities between 5 and 12 feet/sec
  • Line 5. Enter the length of the piping run in feet
  • Line 6. Select the nominal pipe size in inches
  • Line 7. Select the nominal thickness of insulation in inches
  • Line 8. Select an insulation material.
    Note: Calculator does not screen for material temperature limitations.
  • Line 9. Select thermal emittance of the outer jacket material.

Note: NA = Insulation Size Not Available. Some sizes and thicknesses may not be commercially available.


  • One dimensional, steady state heat transfer
  • U-factor constant at average conditions
  • Thermal resistance of film at inner pipe surface neglected
  • Thermal conductivity based on ASTM Specification Values. Refer to the introductory notes for further clarifications.